First alpha of Drupal 7 is available
cmscritic.com
cmscritic.com
Before attempting to upgrade any drupal site to the newest release.
It seems simple in theory but in practice upgrading drupal to a new major release (they call it 'moving') is hard to impossible for any but the simplest sites.
For sites that are not so simple consider building a completely new installation using the drupal version that you intend to use and then migrate your data afterwards using a one-time-use script.